This invention is directed generally to improvements in voltage regulators, and particularly to voltage regulators for use in television receivers.
Conventional television receivers employ a horizontal oscillator which drives a horizontal output transformer across which a high voltage sweep signal is developed. The latter signal is coupled to a cathode ray tube for deflecting the electron beam or beams horizontally.
An AC signal developed by the horizontal output transformer is also frequently rectified and used as a power source for the receiver's regulated DC power supply. The latter supply is usually employed to energize the various circuits within the receiver and to stabilize the power supply for the horizontal oscillator after it has been excited.
The problem which arises with such an arrangement is that the horizontal oscillator must be first energized to excite the horizontal output transformer, and yet the rectified output of the latter transformer is used to develop the regulated DC supply which powers the horizontal oscillator. Clearly, the horizontal oscillator must be at least initially powered by something other than a source developed from the horizontal output transformer if the horizontal oscillator is to be energized at all.
In line-operated receivers, i.e., receivers not employing a power transformer to isolate the receiver from the AC line, diode rectifiers receive the AC line voltage and develop an unregulated DC supply which may be coupled through a resistor or the like to the horizontal oscillator. Hence, the horizontal oscillator is energized as soon as line power is applied to the receiver. However, a considerable amount of power is spent in the resistor. In addition, the voltage energizing the horizontal oscillator is not usually as regulated as is desired.
Other methods for exciting the horizontal oscillator include employing a so-called "start-up" transformer for exciting the horizontal oscillator. The added expense of that approach is, of course, undesirable.
Accordingly, there is a need for a reliable, inexpensive, and efficient regulator for initially energizing the horizontal oscillator in line-operated television receivers and for thereafter driving a regulated DC supply voltage from the horizontal sweep system. In fact, the same need exists for any television receiver whose regulated DC supply is derived from the horizontal sweep system.
A voltage regulator which meets the needs described above will preferably be capable of use in a variety of television receivers. For example, in black and white receivers, the trend is to include most of the low power circuits on a single integrated circuit chip. That same chip would desirably contain a voltage regulator of the type described above.
To obtain maximum use of the single chip, it is desirable that the voltage regulator be usable in receivers that are battery operated as well as in receivers which are operated from a conventional AC source.